The present invention relates generally to the field of stripper/packers on well heads.
A known stripper/packer shown in FIG. 1 has one packing element and a hydraulically actuated window that closes downwardly to provide access to the packer element so that a worn packer element can be replaced. The upper region of the stripper/packer includes a significant amount of wasted space, in which guide bushings must be provided to contain coiled tubing as it is guided through the stripper/packer.
The stripper/packer is installed to contain wellbore pressure and fluids during coiled tubing operations. The stripper/packer provides a means to effect a dynamic seal around moving tubing. A seal is accomplished by an annular packing element being adjustably compressed around the tubing by a hydraulic piston.
As coiled tubing moves through the stripper/packer in contact with the packer element, it wears away the material of the packing element. Thus, the working lifetime of the packing element is of primary concern to operators of coiled tubing systems. The packing element must be replaced when frictional wear has abraded the material to a point that a seal can no longer be accomplished. When the packing element is worn to the point where it can no longer hold a seal (and preferably before this occurs), the packing element must be replaced.
To increase the time between packing element changes, operators have employed two stripper/packers mounted in tandem, effectively doubling the time between packing element changes. The disadvantages of using two stripper/packers are readily apparent, including such drawbacks as added weight, length, and cost. Furthermore, only the upper stripper/packer can be used when snubbing the coiled tubing (i. e. inserting the coiled tubing into the hole) because the coiled tubing typically buckles under compressive stress if the lower stripper/packer is used.
Thus, there remains a need for a stripper/packer which includes two independently replaceable packing elements in the same form factor which currently retains a single packing element.
The present invention addresses this need in the art by adding a second packing element within the same stripper/packer. This invention provides a second packing element, which is interchangeable with the first packing element, thereby minimizing inventory concerns. The actuating hydraulic piston is the same diameter as the lower piston, which allows the operator to utilize the same amount of pressure to maintain a seal during transition between packing elements. Both packing elements are separately actuated from the lower side allowing the wellbore pressure to assist the seal.
In another aspect of the present invention, operators will sometimes allow wellbore fluid to leak by to lubricate the packing element in an effort to extend packer element life. This invention allows the operator to separately apply a small amount of pressure to the upper packing element to act as a wiper and allow the wiped fluid to be collected through the wellbore access port to alleviate environment concerns.
Thus, the present invention provides two independently replaceable packing elements in the same size body as previously used for a single packing element. This structure save size and weight associated with coupling two stripper/packers in tandem. Further, because the upper portion of the stripper/packer body includes a packing element, the upper element can be effectively used during snubbing operations without concern that the coiled tubing will buckle.
These and other features of the present invention will be apparent to those skilled in the art from a review of the following description along with the accompanying drawings.